Field of the Invention
The invention relates to a sensor apparatus, and particularly relates to a capacitor sensor apparatus and a sensing method thereof.
Description of Related Art
A conventional capacitor sensing method may determine a frequency band of a measured single according to a physical characteristic of a tested object. For example, a touch chip may use a frequency band of 50 KHz-300 KHz to measure a capacitance variation. However, in application of an active stylus or fingerprint identification, a frequency band of 1 MHz or 10 MHz is probably used to perform the measurement. In a general capacitor sensor apparatus, a modulation device and a demodulation device perform signal modulation and demodulation according to a same oscillation signal, so that problems of frequency asynchronization and phase asynchronization does not exist. However, in order to prevent a capacitor sensing signal from being influenced by adjacent noise signals, the capacitor sensor apparatus is required to be added with a high-order band-pass filter to effectively filter the noises, though the high-order band-pass filter generally has a high price, such that the manufacturing cost of the capacitor sensor apparatus is greatly increased.
Moreover, another method of preventing the capacitor sensing signal from being influenced by the adjacent noise signals is to configure a band-pass filter behind an analog-to-digital converter (ADC), and since the digital band-pass filter has a low cost compared with that of an analog band-pass filter, the manufacturing cost can be decreased, though such method enhances circuit complexity of the ADC.